Rich executives got richer in 2016, as pay increases remained frozen for the average employee.

Chief executive salaries increased by 6 percent in 2016, according to a survey released Thursday by advisory firm Willis Towers Watson — higher than the 4 percent increase in 2015 and the highest increase since 2013. Wages for executives have been increasing at a relatively moderate rate in recent years — for CEOs, at least. The survey attributed the increase of CEO compensation to uneven corporate performance, increasing annual bonuses and a sharp decrease in the value of stock option exercises.

As chief executives continued to get richer in 2016, the average employee saw only a 3 percent raise in their annual salary last year — the same they received the previous three years. That’s essentially stagnant wage growth, when inflation is taken into account. However, workers whose performance exceeded expectations continued to receive significantly larger raises, the survey found. Still, that may not soothe the frustration of employees who have waiting for bigger raises.

A separate study from industry research group Equilar confirmed the 6 percent raise, but that also highlighted a far more startling difference: the average CEO pay reached $16.6 million in 2016, Equilar found, compared to average annual salary of $49,630 for U.S. workers, according to the Bureau of Labor Statistics.

“Given the substantially higher pay most CEOs enjoy, it is worth a reminder that any raise ends up being huge in dollar terms,” Mark Hamrick, Washington bureau chief at personal finance website Bankrate.com said. “We’re reminded of the long-term challenges of income inequality in the U.S. and the hollowing out of the middle class. Most CEOs are not going to have to worry about saving for retirement or for the college educations of their children.”

In 2016, there were eight CEOs with pay packages exceeding $30 million. Meanwhile, America’s Middle class has been shrinking and lost 30 percent of its wealth over the last four decades, according to another 2015 study. “For many workers, seeing the large pay increases many CEOs are able to command, there’s further insult to financial injury because of the low rate of wage gains overall,” Hamrick said.